1. Field of the Invention
Illustrative embodiments described in this patent specification generally relate to a sheet tray and an image forming apparatus, and more particularly to a sheet tray that facilitates fixing of sheet jams and an image forming apparatus including the sheet tray.
2. Description of the Related Art
Related-art image forming apparatuses, such as copiers, printers, facsimile machines, and multifunction devices having two or more of copying, printing, and facsimile functions, typically form a toner image on a recording medium (e.g., a sheet of paper, etc.) according to image data using an electrophotographic method. In such a method, for example, a charger charges a surface of an image carrier (e.g., a photoconductor); an irradiating device emits a light beam onto the charged surface of the photoconductor to form an electrostatic latent image on the photoconductor according to the image data; a developing device develops the electrostatic latent image with a developer (e.g., toner) to form a toner image on the photoconductor; a transfer device transfers the toner image formed on the photoconductor onto a sheet of recording media; and a fixing device applies heat and pressure to the sheet bearing the toner image to fix the toner image onto the sheet. The sheet bearing the fixed toner image is then discharged from the image forming apparatus.
In general, multiple sheet trays, each detachably attachable to the image forming apparatus and holding recording media, are disposed one above the other in a lower part of the image forming apparatus, below an image forming part of the image forming apparatus. An internal conveyance path extending in a substantially vertical direction is needed for such an image forming apparatus to convey the recording media from the sheet trays to the image forming part of the image forming apparatus disposed above the sheet trays. For good operation and also for ease of servicing, a configuration that facilitates fixing of a sheet jam in the conveyance path is crucial.
In some image forming apparatuses, the sheet trays are attached to and detached from the apparatus in a direction perpendicular to a sheet feeding direction in which sheets are fed from the sheet trays. In other image forming apparatuses, the sheet trays are attached to and detached from the apparatus in the sheet feeding direction. Configurations that facilitate fixing of a sheet jam have been proposed for both types of the image forming apparatuses.
For example, JP-2005-084181-A discloses an image forming apparatus including a sheet tray withdrawable from the apparatus, a lock mechanism that prevents the sheet tray from being withdrawn from the apparatus, a sheet feed unit that feeds a sheet in a direction perpendicular to a direction of withdrawal of the sheet tray from the apparatus, an open/close member provided immediately downstream from the sheet feed unit to open a sheet conveyance path, and a detector that detects presence or absence of the sheet in the sheet conveyance path. When a sheet jam is detected in the sheet conveyance path, withdrawal of the sheet tray from the apparatus is prevented by the lock mechanism. Accordingly, the sheet jammed in the sheet conveyance path is prevented from being torn apart by withdrawal of the sheet tray, thereby preventing the torn sheet from remaining within the image forming apparatus.
However, the above-described configuration is useful only for the image forming apparatus in which the direction of withdrawal of the sheet tray is perpendicular to the sheet feeding direction. Therefore, it is still difficult to access the jammed sheet in the image forming apparatuses in which the direction of withdrawal of the sheet tray is parallel to the sheet feeding direction.
In another approach, JP-2006-184855-A discloses an image forming apparatus including a sheet feeder detachably attachable to the image forming apparatus in a sheet feeding direction, a first conveyance unit that conveys a sheet from the sheet feeder, an image forming unit that forms an image on one side of the sheet conveyed by the first conveyance unit, a second conveyance unit that conveys the sheet having an image formed by the image forming unit, a fixing unit that fixes the image formed on the sheet conveyed by the second conveyance unit, and a return unit that returns the sheet from the fixing unit to an upstream portion from the first conveyance unit so as to form an image on the other side of the sheet. The sheet feeder, the first and second conveyance units, and the return unit are together withdrawable from the image forming apparatus in the sheet feeding direction. The above-described configuration allows easy removal of the jammed sheet from the image forming apparatus without damaging the sheet.
In yet another approach, JP-H07-057650-A discloses an image forming apparatus including a sheet feeder disposed one of above and below an image forming part, a sheet discharger disposed the other one of above and below the image forming part, a substantially vertical sheet conveyance path disposed between the sheet feeder and the sheet discharger via the image forming part, and a conveyance mechanism that conveys a sheet through the sheet conveyance path. A main portion of the image forming part and the sheet feeder are installed in an immovable part of the image forming apparatus, and a conveyance unit including a part of the conveyance mechanism is supported by the apparatus rotatably around a bottom portion of the apparatus. As a result, the conveyance unit is withdrawn from the apparatus to expose the sheet conveyance path to the outside of the apparatus when a sheet jam occurs, thereby facilitating fixing of the sheet jam.
However, in both of the above two image forming apparatuses, a substantial part of the apparatus needs to be withdrawn in order to remove the jammed sheet. Consequently, the withdrawable part must be strong, thereby increasing the weight of the apparatus and inconveniencing the user to fix a sheet jam.